The ever-increasing demand for high-speed data communications services and greater bandwidth is largely due to the popularity of the Internet and other data-intensive, high bandwidth applications. Both businesses and consumers are demanding higher bandwidth connections and faster Internet access. Another source for this demand is the increasing use by businesses of data communications networks (including traffic over the Internet) for the transmission of documents and electronic mail.
Digital Subscriber Loop (DSL) technology provides one approach to addressing the demand for high-speed telecommunications service. DSL technology refers to several types of services that use advanced modem elements to transmit digital signals from a data source over copper wires. Many telephone companies have embraced DSL technology as an immediate broadband solution to serve the current demand by getting more out of their existing copper infrastructure. DSL modem elements permit high data rate transmission of data over the public switched telephone network PSTN) at multiple megabit speeds using sophisticated signal processing techniques that permit voice and data to travel simultaneously over the same analog copper twisted pair wire.
Where DSL modems are arranged in a modem pool such that two or more modem connections are carried via the same copper wire bundle, contending with crosstalk between co-interfering modems becomes an important issue. Moreover, other wire pairs in the bundle are likely to be used by other “alien” services that have nothing to do with the modem pool. In this case, the overall noise within the bundle is likely to be composed of both self-caused crosstalk among modems of the modem pool, as well as crosstalk caused by the alien services. Techniques have been developed to cancel crosstalk from alien services, where the alien crosstalk is first quantified by employing one or more transmission transmission lines within the modem pool as sensors, and then cancelled within the modem pool. However, different combinations of lines as sensors may result in better or worse alien crosstalk cancellation. While testing every possible combination of sensor lines would yield the optimal combination, doing so is impractical given typical operational time constraints. Therefore, techniques for deciding which combinations of lines to designate as sensors without requiring that each possible combination be tried would be advantageous.